German patent document 43 24 970 C2 describes how to create a depth structure in the surface of a silicone-rubber embossing roller. First, an endless positive mold is made from the surface of a pattern. A layer of silicone rubber is then poured or painted on the positive mold. The layer is then vulcanized into an embossing daughter that is removed from the positive mold and bonded to the circumferential surface of the embossing roller with its negative embossing surface facing outward. To produce the endless positive mold, the surface of the pattern is mechanically or optically scanned and the optical information so obtained is converted into a corresponding electrical information, namely a control signal. A layer of material having a surface that permits it to be engraved by an incident laser is mounted on the circumference of a roller. A laser beam is directed onto the surface of the material on the roller. The laser beam and the roller surface are displaced relative to each other and the intensity of the laser beam is modulated as a function of the control signal so that the pattern is engraved by the laser beam into the surface of the roller material. While the engraving faithfulness is very high, a drawback is that the engraved pattern depends upon the original pattern. While it is possible to engrave several embossing rollers using the same control signal, in the prior art the same engraved pattern can be produced only in relation to the original pattern.
German patent document 41 33 620 C1 discloses a method of the pertinent species wherein the apparatus producing a topological depth structure in a workpiece generates a Laser beam guided by a control signal driving a control unit along a dot-determined groove line on the workpiece surface being processed. To determine the groove line, the coordinates of path-curves are first ascertained and then the coordinates or nominal points sub-dividing the path-curves in discrete path segments are ascertained. Thereupon an elliptical or circular surface associated with each nominal point is determined. The groove points contained in the surface are selected arbitrarily. In the end, a control signal is used causing the processing laser beam to move along the groove line in such manner that a corresponding line is produced in the workpiece surface. By appropriately selecting the size of the segments and/or the size of the elliptical or circular surfaces and by many repetitions of these procedures, optionally in different directions, a large number of different and possibly mutually incident lines is generated on the workpiece surface and as a result, a surface structure with approximately uniform roughness is obtained. Even though the control signal of this known method is variable in the sense that the groove lines and thereby the processing lines run in different ways and upon manifold repetition of the processing a plurality of substantial recesses are produced at the crossings of the groove lines, that is are produced at different sites, the appearance of such a surface nevertheless will be uniform and hence monotonous.
The object of the present invention is to create a method for generating an electric control signal driving apparatus to produce topological depths on a workpiece by means of which a control signal generating substantially monotonous surface structures can be generated independently of an original pattern.
The basic concept of the present disclosure is to artificially synthesize the control signal driving the apparatus producing a depth-structure, i.e. a topological structure, from at least two signal components of which the amplitudes and time functions can be selected separately and which may then be additively superposed. In other words, basic and different traits of the topological depth structure can be taken into account when generating each signal component, unlike the case of summarily forming only a single control signal.
Illustratively in an appropriate implementation of the method of the present invention, one signal component may be formed to correspond to a fine structure and another signal component may be formed to correspond to a coarse signal of the desired topological structure. If for instance the desired topological structure is an imitation leather surface, the fine structure can correspond to the pores and the coarse structure to the grain of the surface of natural leather. In addition, a further signal component may be formed for a striated structure. In order to impart some roughness to the surface, it is possible to constitute a signal component in the form of a noise signal. The addition of all these signals results in a control signal to drive a surface processing apparatus, for instance a milling machine, or which may drive the intensity or the speed of displacement of a laser beam in order to create in this manner the topological depth structure of the workpiece.
In a further implementation of the invention the relative amplitudes of the signal components may be varied. Illustratively the pore size may be changed relative to the grain size when generating a control signal to form a topology corresponding to a leather surface and to achieve in this manner various leather imitations.
In a further development of the invention the making of the fine and/or coarse structure is based on a cell structure for which the area being processed is divided into a pattern of surface segments herein called cells which may differ from one another more or less in their absolute and relative sizes and with respect to their boundary lines.
In a further implementation of the invention, cell nuclei are determined arbitrarily or at random with respect to location and mutual spacing and on that basis cell boundaries are determined for the purpose of defining the positions of the individual cells in the cell structure in the direction of the area of the workpiece being processed. The cell boundaries may be formed in a number of ways. One appropriate way is to form the cell boundaries as center-perpendiculars to conceptual lines connecting adjoining cell nuclei. This approach already leads to natural cell patterns, however the boundary lines of the cells are always straight and hence the cells are polygons. In some circumstances this geometry is immediately recognized by the naked eye and thus constitutes a drawback if imitation of pores and/or grain of natural leather is desired.
Accordingly, it is especially appropriate to form the cell boundaries so that they be irregularly and preferably randomly increasing farther away from the cell nuclei. At least two iteration stages may be preset and thereby cell structures of different sizes may be superposed.
Because cells so made only represent areas on the surface of the workpiece being processed, formation of a topological structure requires associating freely or randomly selected height signals which when combined will form the signal components.
In an appropriate implementation of the invention, one of the signal components is formed to correspond to a linear structure composed of linear segments abutting at angles selected in specified or random manner. Because this signal component obviously also is depth signal, recesses shaped like grooves are produced by this signal component in the workpiece surface, where the grooves may corresponds for instance to the folds of natural leather. Appropriately the cross-sectional contours of the particular line segments are predetermined individually or as whole and/or are selected at random from a list of predetermined cross-sectional contours. In this manner small or large folds of natural leather may be imitated.
Lastly and as regards an appropriate implementation of the present invention, a signal component may be formed to correspond to a dot structure. As a result, it is possible for instance to imitate the hair pores of a natural leather surface. In this case as well, the sites and mutual spacings of the points are appropriately selected freely or randomly and advantageously signal elements of a signal component corresponding to each point of the dot structure will be formed corresponding to a bell curve.